11, it hard to explain but it right the pattern is +4 then -3, +5 then -2, add +6 then -1, which would get to 11

The second differences of the given series alternate -7, 8, -7, 8. If the series continues in that way, it looks like

2, 6, 3, 8, 6, 12,

The number 11 is next in the series.

First differences are

4, -3, 5, -2, 6

They would continue as

4, -3, 5, -2, 6,

Effectively, the series can be considered as two interleaved quadratic series.

2, 6, 3, 8, 6, 12,

**11**, 18, 18, 26, 27, 36The number 11 is next in the series.

First differences are

4, -3, 5, -2, 6

They would continue as

4, -3, 5, -2, 6,

**-1**, 7, 0, 8, 1, 9Effectively, the series can be considered as two interleaved quadratic series.

The number which best completes the sequence below is:

2 6 3 8 6 12

2 6 3 8 6 12